An obligate Tay-Sachs disease (TSD) variant carrier (VC) is healthy despite having no demonstrable hexosaminidase A (hex A) activity in her serum, leukocytes and urine. Hex A is present in her tears, saliva and cultured skin fibroblasts and presumably in her nervous system. Her fibroblast hex A has an exceedingly low Vmax, while the Km toward synthetic substrates is normal or a little lower (better binding of substrate). This apparent Vmax is exaggerated because of thermal activation of hex A at 37 degrees for lengths of time even loger than the assay. Partially purified fibroblast VC and control hex A and hex B will be further characterized for: 1. recognition and uptake by hex A-and/or B- deficient cell lines, 2. binding to lectins, 3. secreted enzymes in the medium, 4. pH optima, 5. electrophoretic mobility, 6. isoelectric focusing, 7. molecular weight, 8. subunit dissociation and aggregation with merthiolate or freeze-thawing in concentrated sodium chloride, 9. kinetic parameters of substrates and inhibitors, 10. energy of activation, 11. immunological properties and quantitation. Attempts will be made to induce hex A expression in lymphocytes stimulated with phytohemagglutinin. The purpose of the investigation is to: 1. illuminate the nature of variable tissue hex A expression when classical genetics dictates a single gene controls hex A expression in all tissues, and 2. augment the understanding of the scope of variant enzyme expression, and 3. help differentiate in vitro distinction of the physiological functionality of hex A alleles.